This invention relates to lasers, and more particularly, it relates to a multiple wavelength ammonia laser pumped by a carbon dioxide laser.
Recently there has been increased interest in laserpumped lasers wherein a laser beam from a first laser is used to pump a second laser which provides the desired output beam. This type of laser finds application in a number of fields including isotope separation, laser photochemistry, high resolution spectroscopy, and air pollution monitoring.
In the foregoing and other applications it is often necessary to utilize a laser beam at a particular frequency. Since the frequency of a laser beam depends upon the energy level structure of the medium used in generating the beam, if one desires a laser beam at a particular frequency he must select the particular laser that most closely fits the desired frequency condition. Since there are some desired frequencies which do not match any laser output frequency, a need exists for developing lasers which can be tuned to provide an output at any desired frequency in a range of frequencies.
In the case of a gas laser, tunability can usually be enhanced by increasing the pressure of the gaseous working medium and thereby Lorentz broaden the linewidth of the lasing transition. Since lasers excited by means of an electric discharge have a tendency to arc at high operating gas pressures, and since some laser beams are closely matched in energy to absorbing transitions in certain laser gases, laser-pumped lasers offer great potential for providing tunable lasers of high efficiency and reliability.
One particular laser-pumped laser combination which is receiving attention in the scientific community involves optically pumping ammonia (NH.sub.3) with the output from a carbon dioxide (CO.sub.2) laser. Carbon dioxide lasers are not only readily available, but these lasers provide output wavelengths near ammonia absorption resonances. In fact, both the absorption spectra of the ammonia molecule and the output lines from carbon dioxide lasers have been studied extensively and are well tabulated (see, for example, J. S. Garing et al, "The Low-Frequency Vibration Rotation Bands of the Ammonia Molecule", Journal of Molecular Spectroscopy, Vol. 3 (1959), pages 496-527; T. Y. Chang, "Accurate Frequencies and Wavelengths of CO.sub.2 Laser Lines", Optics Communications, Vol. 2, No. 2 (July 1970), pages 77-80; and E. D. Hinkley et al "Long-Path Monitoring: Advanced Instrumentation with a Tunable Diode Laser", Applied Optics, Vol. 15, No. 7 (July 1976), pages 1653-1655).
In recent years a variety of ammonia lasers have been developed pumped by different carbon dioxide laser lines and providing respective outputs at different ammonia transistion wavelengths. Initially, ammonia output wavelengths were obtained generally in the 30 .mu.m to 400 .mu.m range (see K. Gullberg et al, "Submillimeter Emission from Optically Pumped .sup.14 NH.sub.3 ", Physica Scripta, Vol. 8 (1973), pages 177-182). More recently, several additional ammonia output lines have been achieved at shorter wavelengths ranging from 11.46 .mu.m to 12.81 .mu.m (see T. Y. Chang et al, "Laser Action at 12.812 .mu.m in Optically Pumped NH.sub.3 ", Applied Physics Letters, Vol. 28, No. 9 (May 1, 1976), pages 526-528; E. J. Danielewicz et al, "High-Power Vibration-Rotation Emission from .sup.14 NH.sub.3 Optically Pumped Off Resonance", Applied Physics Letters, Vol. 29, No. 9 (Nov. 1, 1976), pages 557-559; and T. Y. Chang et al, "Off-Resonant Infrared Laser Action in NH.sub.3 and C.sub.2 H.sub.4 Without Population Inversion", Applied Physics Letters, Vol. 29, No. 11 (Dec. 1, 1976), pages 725-727).
A particular carbon dioxide laser line which has been useful in pumping ammonia to produce laser radiation at 12.08 .mu.m as well as at 67 .mu.m is the R(30) carbon dioxide laser line at 9.2 .mu.m. However, in the past, neither the R(30) line nor any other carbon dioxide laser line had ever produced a plurality of ammonia lines emanating from respective energy substates characterized by different values of the rotational quantum number K (which represents the component of molecular angular momentum about the unique axis of the molecule).